1. Field of the Invention
The present invention relates to an optical communication system, and more particularly to a cross-connection device for use in an optical communication system employing wavelength-division-multiplexed optical signals.
2. Description of the Related Art
Cross-connection devices are used in optical communication systems for cross-connecting a plurality of wavelength-division-multiplexed optical signals inputted from a plurality of input ports, i.e., redistributing such optical signals depending on the destination information and outputting newly wavelength-division-multiplexed optical signals from respective output ports. Such cross-connection devices are disclosed in Japanese laid-open patent publication No. 7-162904 published Jun. 23, 1995 and U.S. Pat. No. 4,821,255, etc.
One typical prior cross-connection device is shown FIG. 1 of the accompanying drawings.
As shown in FIG. 1, the conventional cross-connection device comprises m input ports 101.about.10m for being supplied with respective wavelength-division-multiplexed optical signals each comprising multiplexed n different wavelengths .lambda.1.about..lambda.n, m demultiplexers 111.about.11m for demultiplexing the wavelength-division-multiplexed optical signals from the m input ports 101.about.10m into individual optical signals having the respective wavelengths .lambda.1.about..lambda.n, a routing circuit 120 for cross-connecting a total of m.times.n optical signals including n optical signals outputted from the respective demultiplexers 111.about.11m, m multiplexers 131.about.13m for multiplexing optical signals of n wavelengths .lambda.1.about..lambda.n from the routing circuit 120, and m output ports 141.about.14m for outputting wavelength-division-multiplexed optical signals from the multiplexers 131.about.13m.
The routing circuit 120 converts the m.times.n optical signals into optical signals of the same or other wavelengths depending on the destination information, and cross-connects the optical signals for thereby redistributing them in groups of m wavelength-division-multiplexed optical signals.
While the conventional cross-connection device can be incorporated in large-scale optical communication systems, it necessarily suffers an increase in circuit scale because it is required to divide inputted wavelength-division-multiplexed optical signals into optical signals of the respective wavelengths, cross-connect them, and multiplex them again for outputting wavelength-division-multiplexed optical signals.
If the number of wavelengths to be multiplexed is 4, then the multiplexers and demultiplexers cause a total of losses of 12 dB, 6 dB by the multiplexers and 6 dB by the demultiplexers, even with ideal filters used, resulting in a substantial reduction in the power of optical signals.